Processes for preparing organic compounds having improved color characteristics

ABSTRACT

Carboxylic acids, ketones, and esters having improved color characteristics are produced by combining small quantities of water with these compounds. An amount of water ranging from about 100 ppm to about 50,000 ppm of the organic compound is combined to provide lighter color compounds in comparison to these same compounds to which no water is added. Additionally, the color characteristics of the organic compounds may be improved by introducing a stream of the organic compound into at least one distillation column maintained at a temperature of about 23° C. to about 250° C. and at a pressure of about 10.1 kPa to about 202.6 kPa. Subjecting the organic compound stream to distillation under these conditions allows precursors of color bodies, having boiling points lower than the boiling point of the product being produced, to thermally breakdown or to be removed in the overhead stream form the distillation column.

RELATED APPLICATIONS

This is a divisional application of prior U.S. application Ser. No.10/635,983 filed on Aug. 7, 2003, the disclosure of which isincorporated herein by reference.

FIELD OF THE DISCLOSURE

This disclosure relates to processes for preparing carboxylic acids,ketones, and esters having improved color characteristics.

BACKGROUND INFORMATION

There are numerous known processes for producing carboxylic acids,ketones, and esters. For example, U.S. Pat. Nos. 3,887,595, and6,211,405 disclose processes for producing carboxylic acids bycarbonylating olefinically unsaturated compounds such as alcohols,ethers, and esters. U.S. Pat. No. 5,281,752 discloses a process forproducing lower carboxylic acids by reacting alkanes with carbondioxide. U.S. Pat. No. 5,091,587 discloses a process for the preparationof ketones which comprises reacting a conjugated diolefin and water inthe liquid phase in the presence of a catalyst system comprising: agroup VIII metal compound and a source of protons. U.S. Pat. No.4,010,188 discloses a process for the oxidation of saturatedhydrocarbons in the presence of a catalyst to produce acids. U.S. Pat.No. 3,293,292 discloses a liquid phase oxidation of butane in thepresence of a cobalt containing catalyst system to produce carboxylicacids. U.S. Pat. No. 4,487,720 discloses a process of the production ofacids by oxidizing saturated aliphatic aldehydes in the presence ofcatalyst systems. U.S. Pat. No. 5,026,903 discloses a process forproducing of glycol esters such ethylidene diacetate by the reaction ofmixtures of dimethyl acetal, methyl acetate and carbon monoxide. Thecatalyst system charged to the reactor contains rhodium atoms, lithiumiodide and optionally an organic ligand. U.S. Pat. No. 4,268,689 alsodiscloses a process for the production of glycol esters.

A problem associated with carboxylic acids, ketones, and estersproduction and storage is color quality. To use carboxylic acids andother organic compounds for certain applications, the compounds mustexhibit a light color. Generally speaking, the darker color values forthese organic compounds do not affect the functionality of the compoundsfor most applications. However, most purchasers of these organiccompounds believe that “water white” compounds are of higher qualitythan compounds possessing higher color properties and demand water whiteorganic compounds. Typically, compounds exhibiting an APHA color (Pt—Co)of 15 or less are considered to be of water white quality. If thecompounds are not of a water white quality, expensive purificationschemes must be undertaken to purify the product to achieve acceptablecolor characteristics. For example, expensive and multiple hydrogenationand acid treatment processes may be necessary to achieve a compoundhaving water white characteristics.

BRIEF DESCRIPTION OF DISCLOSURE

This disclosure relates to processes for preparing certain organiccompounds such as carboxylic acids, ketones, and esters having low colorcharacteristics. A first embodiment involves combining water with theorganic compound at a concentration of 100 ppm to 50,000 ppm water. Asecond embodiment involves removing a product stream containing theorganic compound from a reaction system in which the organic compound isprepared and introducing the product stream into a distillation columnhaving a lower portion and an upper portion wherein the upper and lowerportions are maintained at a temperature of from about 23° C. to about250° C. and at a pressure of about 10.1 kPa to about 202.6 kPa.Subjecting the product stream to distillation under these conditionsthermally breaks down, or removes, precursors of color bodies, havingboiling points lower than the boiling point of the product beingproduced.

A third embodiment includes combining the process of the first twoembodiments by producing a product that has been subjected to isolationand purification in a system including a distillation column operatingat the temperatures and pressures described above and combining waterwith the organic compounds as described above.

These processes may be implemented to prepare carboxylic acid, ketone,and glycol ester products having stable APHA color values of 15 or less.Having a stable APHA color of 15 or less means that the products willexhibit a color value within this range after being boiled for at leastone hour at one atmosphere (101.3 kPa) pressure.

DRAWING

FIG. 1 is a schematic diagram of an embodiment of the process of thisinvention.

DETAILED DISCLOSURE

This disclosure relates to processes for preparing certain carboxylicacids, ketones, and esters having low color properties. The organiccompounds include C₁ to C₆ carboxylic acids, ketones having boilingpoints from 54° C. to 170° C., and esters having boiling points fromabout 168° C. to about 250° C. These various organic compounds may bethe reaction product of a variety of processes for producing thesecompounds. For example, carboxylic acids are often commercially preparedby carbonylation of alcohols, esters, or ethers to produce thecorresponding carboxylic acid. A widely used commercial carbonylationprocess is the production of acetic acid from carbonylation of methanol.Of course, the carbonylation process is applicable to the carbonylationof higher homologues of methanol to form acids that are the higherhomologues of acetic acid. The carboxylic acids useful in thepreparation process described in this disclosure may be the reactionproduct of other processes such as oxidizing corresponding aldehydes,alkanes, and alkenes.

Additionally, the processes described here may also be used to preparelow color value carboxylic acids that are prepared by reacting alkaneswith carbon monoxide in the presence of palladium and/or coppercatalysts and salts of peroxy acids. The carboxylic acids may also beproduced thorough the oxidation of saturated alkanes. For example, thisoxidation process may be used to produce butyric acid through theoxidation of butane.

In summary, the C₁ to C₆ carboxylic acids produced by any process,including but not limited to the exemplary processes referred to in theBACKGROUND INFORMATION above, may exhibit improved color properties as aresult of the color improvement processes described in this disclosure.

Any process, including but not limited to the exemplary processesreferred to in the BACKGROUND INFORMATION above, may also produce theketones and esters that exhibit improved color characteristics as aresult of the processes described herein.

An exemplary process scheme for the production of carboxylic acids isdepicted in FIG. 1. Specifically, the process depicted in FIG. 1 is forthe production of butyric acid through the oxidation of butane. It isunderstood that the process scheme depicted may be used to produce avariety of other carboxylic acids, including, but not limited to, aceticacid, through the oxidation of naptha, pentane, and other feedstocks. Aliquid phase reactor 10 is charged with air or oxygen content enrichedair. The oxygen content of the feed may be at any level, including pureoxygen. Of course, when using pure oxygen or highly enriched air,appropriate safety precautions should be observed to prevent fire orexplosion hazards. However, in terms of a balance of reaction efficiencyand economics, generally an enriched air feed having an oxygen contentfrom about 20% to about 30% is found to be useful. The reactor 10 isalso charged with pure butane although a stream contain less than purebutane may be used provided the process scheme used can accommodateremoval of any impurities included with the butane.

The butane is oxidized in the presence of any suitable oxidationcatalyst. An exemplary catalyst is cobalt salt catalyst present at aconcentration of less than 5,000 ppm. Additionally, recycle steams asdescribed hereinafter, may be routed to the reactor. As the reactionproceeds, the reactor should be maintained at temperature from about100° C. to about 200° C. and a pressure from about 6.20 Pa to about 6.89Pa. If the feed is naptha, the pressure should be maintained form about3.44 Pa to about 5.51 Pa. A crude product stream 15 is withdrawn as asidestream 15 from the reaction zone and introduced into a firstdistillation column 20 maintained at a bottom portion temperatureranging up to about 200° C. and a top portion temperature ranging fromabout 100° C. to about 120° C. and a pressure of about 10.13 kPa toabout 101.3 kPa to separate an overhead light ends stream 25 and a heavyends cut 30. The light ends stream 25 containing alcohols is recycled tothe reactor 10 and the heavy ends cut 30 is primarily waste product andmay be disposed of by any suitable means, including burning. A productstream 35 is withdrawn as sidestream 35, which is introduced into afirst treatment unit 40. The treatment taking place in unit 40 may beany suitable hydrogenation treatment to improve the properties of theproduct stream 35. A treated product stream 45 is withdrawn formtreatment unit 40 and introduced into a second treatment unit 50 whichmay be any suitable treatment step to remove impurities in the productstream, such as 3-hydroxy 2-butanone. Suitable treatment methods arenitric acid oxidation treatment processes that are well known, such asreferred in U.S. Pat. No. 6,590,129. A treated product stream 55 is thenwithdrawn from treatment unit 50 and introduced into a seconddistillation column 60 maintained at a bottom portion temperature offrom about 100° C. to 200° C. and a pressure of 10.13 kPa to 101.3 kPa.A heavy ends cut 70 containing primarily gamma butyrolactone andcrotonic acid is removed from the bottom of the second distillationcolumn 60. The heavy ends cut may be recycled to the reactor 10. Anoverhead product stream 65 is taken from the second distillation column60. The overhead contains primarily propionic acid and acetic acid andis recycled to reactor 10. The product stream 65 is routed to a thirdtreatment unit 55. The product stream 65 is heated in the thirdtreatment step. In one embodiment, the heat treatment involves boilingthe product stream for an average residence time of one hour atatmospheric pressure. The boiling point for the product stream isapproximately 165° C. The heat treatment step will have the effect ofaccelerating adverse color producing reactions that might occur uponnormal aging of the product. The heat treatment step may also removecertain impurities through cracking or polymerization mechanisms. Atreated stream 80 is withdrawn from the third treatment unit 75 andintroduced into a third distillation column 85 maintained at a bottomportion temperature of up to 200° C. and a top portion temperature of upto 150° C. and a pressure of 10.13 kPa to 101.3 kPa to separate thebutyric acid product from remaining light ends 90 and heavy ends 95 asthe product is withdrawn as sidestream 100 from the third distillationcolumn. Optionally, the product butyric acid stream may be cooled.

As mentioned previously, it is desirable for many purchasers andapplications that the butyric acid, ketones, and esters described hereinhave low color values. An established method for determining the colorof light colored liquids such as these organic compounds is to determinethe APHA number or the liquid. The lower the APHA color value, the morecolorless the liquid. The procedure for determining APHA color number isset forth in ASTM D1209-62 T and E 202-62T. With respect to C₁ to C₆carboxylic acids, low color values means acids having stable APHA colorsof less than or equal to 15. For ketones, low color refers to stableAPHA color values of less than or equal to 15 and for esters, low colorrefers to stable APHA values of less than or equal to 15.

In the butyric production process depicted in FIG. 1, typical finishedproduct APHA color values may range from about 0 to about 5. But, thecolor values of the product often increase over time as the product agesunder typical storage conditions. Often the color degradation isintensified upon exposure of the organic compounds to heat.

To provide a product having desirable low color values, it may benecessary to undertake expensive and time consuming additionalpurification steps to produce a low APHA color value products. It hasbeen unexpectedly determined that stable low APHA color value carboxylicacid, ketone, and glycol ester products may be consistently producedwithout the need for additional expensive and time consumingpurification steps. The low color value products may be produced througheach of the two different processes described in this disclosure andthrough the use of a combination of the two processes.

In a first embodiment, the stable color values of the organic compoundsare improved by combining a small amount of water with the productorganic compounds. In one embodiment, the water is added directly to thefinished organic compound product under conditions of agitation, such asstirring. In another embodiment, the water may be conveniently added bysimply adding the water to an empty mixing vessel and then adding theorganic compound to the vessel. The addition of the organic compoundwill typically provide sufficient mixing energy to form a mixed solutionhaving a consistent concentration of water. The water may be added tothe organic compounds over a wide range of temperatures. For example,the water and the organic compounds may be combined at any temperaturethe water and the organic compound are in liquid phases. In general,when the organic compound is butyric acid, in one embodiment, the waterand butyric acid may be combined at a temperature of from about 0° C. toabout 160° C., depending on the pressure of the system in whichcombining the water and butyric takes place. In one embodiment, thewater and butyric acid are combined at a temperature of about 20° C. toabout 50° C.

In one process, the water is combined with the C₁ to C₆ carboxylicacids, ketones having boiling points from 54° C. to 170° C., and estershaving boiling points from about 168° C. to about 250° C. until aconcentration of about 100 ppm water to about 50,000 ppm water isachieved. In another embodiment, water is combined with a butyric acidproduct to provide a water concentration of about 100 ppm to about10,000 ppm. In still another embodiment, water is combined with butyricacid to achieve a concentration of about 500 ppm water to about 1000 ppmwater.

As mentioned, the water may be combined with the organic compounds underconditions of agitation to achieve uniform distribution of the waterthroughout the organic compound product to provide a more uniformconcentration of the water throughout the organic compound.

Alternatively, water may be added to the organic compound products byadding water in an overhead cut product stream of any conventionalproduction process for producing the organic compounds. For example,with reference to FIG. 1, water may be added to overhead stream 65 toachieve the beneficial color characteristics described in thisdisclosure.

EXAMPLES

The following Examples demonstrate the color characteristics improvementbenefits resulting from adding water to a butyric acid product.

Example 1

A commercially produced butyric acid was found to have an APHA colorvalue of 4. A first sample of the butyric acid was boiled for one hourand found to have an APHA color of 31 after boiling. Water was added toa second sample of the same commercially produced batch of butyric acid,while stirring at room temperature, until a concentration level of 1000ppm water was reached. The water containing second sample was thenboiled for one hour in the same manner as the first sample. Followingboiling, the APHA color value of the second sample was determined to be12.

Examples 2-4

The effect of color degradation through aging was determined on threesamples from a commercially produced butyric acid run. The samples wereprepared by successive distillations of the same portion of thecommercially produced butyric acid run. The APHA colors of the sampleswere determined to be as follows:

Example 2 8 Example 3 4 Example 4 4

The color variance of the samples is attributable to the fact that morecolor bodies were present in the first distillation sample as comparedto the second and third distillation samples.

Each sample was allowed to stand at room temperature undisturbed for 24hours and the APHA colors of the samples were determined as follows:

Example 2 20 Example 3 2 Example 4 9

Examples 5-7

The effect of color improvement though the addition of water wasdetermined on three samples from a commercially produced butyric acidrun. The samples were prepared by successive distillations of the sameportion of the commercially produced butyric acid run. The APHA colorsof the samples were determined to be as follows:

Example 5 13 Example 6 3 Example 7 1

The color variance of the samples is attributable to the fact that morecolor bodies were present in the first distillation sample as comparedto the second and third distillation samples.

To each of these samples was added 20,000 ppm, water while stirring atroom temperature, to ensure uniform distribution of the water. Followingaddition of the water, the APHA colors of the samples were determined asfollows:

Example 5 1 Example 6 1 Example 7 1

A second process by which the color of C₁ to C₆ carboxylic acids,ketones having boiling points from 100° C. to 170° C., and esters havingboiling points from about 168° C. to about 250° C. may be improved isthe use of high temperature conditions during the separation andpurification of product streams of these organic compounds. It has beendetermined that introducing a product stream of the organic compoundinto a distillation column having a lower portion and an upper portionwherein the upper and lower portions are maintained at a temperature ofabout 23° C. to about 250° C. and at a pressure of about 10.1 kPa toabout 202.6 kPa such that precursors of color bodies having boilingpoints lower than the boiling point of the product being produced maythermally broken down or removed in the overhead of the distillationcolumn. The stream may be introduced into one or more distillationcolumns operating under these outlined conditions.

An exemplary embodiment is seen by reference to FIG. 1. Colorimprovement of the butyric acid product may be achieved by operating thefirst distillation column 20, the second distillation column 60, or thethird distillation column 85 the upper and lower portions at atemperature of about 23° C. to about 250° C. and at a pressure of about10.1 kPa to about 202.6 kPa. Subjecting the product stream todistillation under these conditions allows precursors of color bodies,having boiling points lower than the boiling point of the product beingproduced, to be removed in the overhead stream from the distillationcolumn.

In another embodiment, one of the distillation columns may be operatedat upper portion and lower portion temperatures of 170° C. to about 180°C. and at pressures of about 101 kPa to about 202 kPa to improve colorcharacteristics of the butyric acid. Alternatively, all three or any twoof the distillation columns may be operated at the above-statedconditions to achieve color improvement.

In addition to using the water addition process for color improvementoutlined above alone or the high distillation column temperature processdiscussed above in isolation, the improved color characteristics may beobtained by using the water addition and high distillation temperatureprocesses in combination with each other. An additional benefit of usingthe heat treatment step is the removal of low boiling impurities.

Without being bound by theory, it is believed that the processesdisclosed herein obtain improved color properties of the organiccompound products through thermally breaking down, removing, orpreventing the formation of certain color bodies, or precursors to thecolor bodies, during the processes for producing the organic compoundsof interest. Specifically, it is believed that color degradation derivesfrom the formation of Michael Adducts during the production of theorganic compounds in accordance with this description.

It is believed that a compound formed from an unsaturated ketone and acarboxylic acid in the production of the relevant organic compoundsleads to formation of a Michael Adduct in accordance with the followingreaction process:

As seen from this reaction process, the Michael adduct, upondehydration, yields color bodies thought to lead to the undesirabledarker color products. It is believed that by adding water to theorganic compound products, formation of the color bodies is prevented.With respect to the second process involving operating the distillationcolumn or columns during recovery of the organic compounds at thedescribed temperatures and pressures, a different mechanism, accountsfor color improvement in the organic compounds produced. In thisprocess, the intermediate product that is a precursor of the MichaelAdduct may be broken down thermally, thereby preventing the ultimateformation of the offensive color bodies in the organic compoundproducts. Alternatively, the color precursor may be removed in theoverhead of the distillation column as long as the precursor boils at alower temperature than the desired product organic compound.

All patents and publications referred to herein are hereby incorporatedby reference in their entireties.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions, andalterations could be made without departing from the spirit and scope ofthe invention as defined by the following claims.

1. A process for preparation of an organic compound, having a stableAPHA color value of 15, or less selected from the group consisting of C₁to C₆ carboxylic acids, ketones having boiling points from 154° C. to170° C., and esters having boiling points from about 168° C. to about250° C., comprising removing a product stream comprising the organiccompound from a reaction zone in which the organic compound is preparedand introducing the product stream into a distillation column having alower portion and an upper portion wherein the upper portion and thelower portion are maintained at a temperature of about 23° C. to about250° C. and at a pressure of about 101 kPa to about 202.6 kPa.
 2. Theprocess of claim 1 wherein the organic compound is a C₁ to C₆ carboxylicacid.
 3. The process of claim 2 wherein the carboxylic acid is butyricacid.
 4. The process of claim 3 wherein the distillation column isoperated at a temperature of about 170° C. to about 180° C. and at apressure of about 101 kPa to about 202 kPa.